Extension and Revision of the von Baeyer System for Naming Polycyclic Compounds (Including Bicyclic Compounds)
(IUPAC Recommendations 1999)

VB-8.3 to VB-8.5

Continued from VB-8.1 and VB-8.2

Contents of Section

VB-8 Naming Modified Ring Systems (Heteroatoms, unsaturation, stereochemistry, etc.) continued

VB-8.3 Unsaturation
VB-8.4 Prefix Substituents
VB-8.5 Stereochemistry
References for this Section

VB-8.3 Low locants are allocated for double bonds where the atoms of each double bond have consecutive locants. Only the lower of the two locants for each double bond is cited when they differ by one. If the two locants are not consecutive a compound locant is required, see VB-8.3.1. If a triple bond is present see VB-8.3.3.


not bicyclo[3.2.1]oct-3-ene (2 is lower than 3)

However bicyclo[2.2.2]oct-5-en-2-yl
not bicyclo[2.2.2]oct-7-en-2-yl (5 is lower than 7)
nor bicyclo[2.2.2]oct-2-en-5-yl (2 is lower than 5 for free valence, see VB-8.1.3)

If there is a choice of names or numbering the following criteria are considered in order until a decision is made.

VB-8.3.1 A minimum number of compound locants are selected. A compound locant is used for a double bond if the locants of the atoms at each end of the double bond do not differ by one. When a compound locant is required the higher locant is cited in parentheses. A benzene ring is named as a cyclohexatriene corresponding to the Kekulé structure with the preferred name. Other aromatic rings are treated similarly when necessary.

Note This rule was used in the Nomenclature of Steroids (ref 14) rule 3S-2.5(2) e.g. estra-5,7,9-triene is recommended rather than estra-5(10),6,8-triene.


bicyclo[4.2.0]oct-6-ene (also CAS index name)
not bicyclo[4.2.0]oct-1(8)-ene (single locant rather than compound locant)

not bicyclo[6.5.1]tetradec-1(13)-ene (this is a change from R-3.1.1, ref 7)

not bicyclo[12.2.2]octadeca-1(17),14(18),15-triene (1 compound locant rather than 2)

Note This example from A-31.3 (ref 6) is named there as bicyclo[12.2.2]octadeca-1(16),14,17-triene or bicyclo[12.2.2]octadeca-14,16(1),17-triene. The latter name, which is no longer recommended, corresponds to the CAS index name (bicyclo[12.2.2]octadeca-14,16,17-triene). CAS always orientates a ring system so that the main ring is numbered clockwise and thus the aromatic ring is numbered round the ring clockwise. A compound locant is not used by CAS when the second atom is obvious.

bicyclo[4.2.0]octa-1,3,5-triene (also CAS index name)
not bicyclo[4.2.0]octa-1(6),2,4-triene (all single locants selected)

3-thiabicyclo[3.3.1]nona-1(9),5,7-triene (also CAS index name)
not 3-thiabicyclo[3.3.1]nona-1(8),5(9),6-triene (1 compound locant rather than 2)

However bicyclo[5.5.1]tridec-1(12)-en-3-yl
not bicyclo[5.5.1]tridec-1-en-11-yl (3 is lower than 11, see VB-8.1.3)

VB-8.3.2 When comparing double bond locants including compound locants any numbers in parentheses are ignored.


not tricyclo[,8]hexadeca-4(16),5,7-triene
nor tricyclo[,8]hexadeca-4,6,8(16)-triene (1,11,13 is lower than 4,5,7 or 4,6,8)
nor tricyclo[,8]hexadeca-1(14),11(15),12-triene (1 compound locant rather than 2, see VB-8.3.1)

not tricyclo[,8]hexadeca-1(15),4,6,8(16),11,13-hexaene (CAS index name) [1,4,5,7,11,13 is lower than 1,4,6,8,11,13]
nor tricyclo[,8]hexadeca-1(14),4,6,8(16),11(15),12-hexaene (2 compound locants is lower than 3, see VB-8.3.1)
nor tricyclo[,8]hexadeca-1(14),4(16),5,7,11(15),12-hexaene (2 compound locants is lower than 3, see VB-8.3.1)

If there is still a choice low locants are selected considering all locants as a set.


nt tetracyclo[,6.110,13]heptadeca-3(17),10-diene (3,10,16 is lower than 3,10,17)

Note Under some circumstances (e.g. ref 15) localised double bonds have been recognised in an apparently fully conjugated ring. The specific localisation of the double bonds can be indicated by the prefix [Delta] with a superscript locant (or compound locant) of the lowest numbered relevant double bond (see FR-9.2, ref 12; footnote to B-1.2, ref 6).



VB-8.3.3 If there are both double and triple bonds present lower locants are selected for multiple bonds as a set, then lower locants for the double bonds.


not bicyclo[7.3.1]trideca-5,11-diene-3,7-diyne (2,4,6,10 is lower than 3,5,7,11)

not bicyclo[11.2.1]hexadeca-4,11-diene-2,9-diyne (both 2,4,9,11 but 2,9 is lower than 4,11)

However bicyclo[7.2.1]trideca-4,6,9-trien-2-yne
not bicyclo[7.2.1]trideca-1(12),3,5-trien-7-yne (no compound locant, see VB-8.3.1)

VB-8.4 Lower locants are allocated for substituents cited by prefixes.


not 8,8-dimethylbicyclo[2.2.2]octan-2-one (5,5 is lower than 8,8)

not 2,4-dimethoxybicyclo[2.2.1]heptane (1,3 is lower than 2,4)

VB-8.4.1 Low locants are allocated for substituent prefixes in the order of their citation.


not 8-ethyl-5-methylbicyclo[2.2.2]oct-2-ene (5-ethyl is lower than 8-ethyl)

VB-8.5 R is selected rather than S to indicate configuration.


not (1S,2S,4R,5R)-3-oxa-9-azatricyclo[,4]nonane (1R rather than 1S)
Beilstein name = (1rN9,2tH,4tH)-3-oxa-9-azatricyclo[,4]nonane
CAS index name = (1[alpha],2[beta],4[beta],5[alpha])-3-oxa-9-azatricyclo[,4]nonane

Note The above example could also be described as exo- by extrapolation of the term used to describe substituents on a bicyclic bridge compound. Similarly the example below would be endo-. However this system is not recommended as it would be difficult to extend it to tetracyclic systems and even tricyclic systems where it is difficult to identify the bicyclic system used to identify exo/endo.

not (1S,2R,4S,5R)-3-oxa-9-azatricyclo[,4]nonane (1R rather than 1S)
Beilstein name = (1rN9,2cH,4cH)-3-oxa-9-azatricyclo[,4]nonane
CAS index name = (1[alpha],2[alpha],4[alpha],5[alpha])-3-oxa-9-azatricyclo[,4]nonane

References for this Section

6. International Union of Pure and Applied Chemistry, Nomenclature of Organic Chemistry, Sections A, B, C, D, E, F and H, 1979 edition, Pergamon Press, Oxford, 1979.

7. International Union of Pure and Applied Chemistry, A Guide to IUPAC Nomenclature of Organic Compounds, Recommendations 1993, Blackwell Scientific Publications, Oxford, 1993.

12. IUPAC Commission on the Nomenclature of Organic Chemistry, Nomenclature of fused and bridged fused ring systems (IUPAC recommendations 1998), Pure Appl. Chem., 70, 143-216 (1998).

14. IUPAC-IUB Joint Commission on Biochemical Nomenclature, Nomenclature of Steroids (Recommendations 1989), Eur. J. Biochem., 186, 429-458 (1989); Pure Appl. Chem., 61, 1783-1822 (1989) and in Dictionary of Steroids (eds R.A. Hill, D.N. Kirk, H.L.J. Makin and G.M. Murphy) Chapman and Hall, London, 1991, pp xxx-lix; IUBMB, Biochemical Nomenclature and Related Documents, second edition, Portland Press, London, 1992, pp 192-221.

15. L.A. Paquette, M.A. Kesselmayer, G.E. Underiner, S.D. House, R.D. Rogers, K. Meerholz and J. Heinze, Multifaceted consequences of holding two [8]annulene rings face-to-face. Synthesis, structural characteristics, and reduction behaviour of [22](1,5)cyclooctatetraenophane, J. Am. Chem. Soc., 114, 2644-2652 (1992).

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